Numerous vehicle systems are known in the art for controlling the climate of the vehicle passenger compartment. In controlling the climate, it is crucial to control the rate at which air is introduced to the passenger compartment. However, many variables (e.g. vehicle speed) effect input air flow.
U.S. Pat. No. 3,403,855 discloses a system for damping an outside air intake port as a function of vehicle speed. A voltage proportional to the road speed of the vehicle is generated for controlling the opening and closing of an air shutter and thus regulating the ingress of air into the passenger compartment, as well as for controlling the operation of the motor fan.
U.S. Pat. No. 3,861,282 discloses a system for controlling fan motor speed as a function of vehicle speed and reducing the supply of fresh air into the interior space of the vehicle at slow driving speeds or during standstill thereof where large amounts of exhaust gases can pose safety risks.
U.S. Pat. No. 4,858,676 discloses a system where the fan speed is varied in response to the ram air intake at the front of the vehicle. Fan speed is controlled by varying the voltage supplied to the motor driving the fan.
U.S. Pat. No. 4,941,525 discloses a system where the fan speed is varied to maintain a desired temperature inside the vehicle and is also controlled by varying the voltage supplied to the fan motor.
U.S. Pat. No. 4,996,849 discloses a system for positioning a flapper in the fresh air duct.
U.S. Pat. No. 5,102,041 discloses a system in which an air flow is varied to maintain a constant temperature within the passenger compartment and the fan speed is controlled by varying the voltage fed to the fan motor.
U.S. Pat. No. 5,162,709 discloses a system using pulse width modulation to control the speed of a car's air conditioning fan motor. Speed of the motor is varied to eliminate an audible "beating" phenomenon associated with PWM controlled brushless fan motors.
Japanese Patent No. 60-78815 discloses a system in which electrical power fed to an climate control system blower is reduced upon the opening of the vehicles windows.
It is generally known that the air delivered out of the climate control system of a moving vehicle can be affected by the pressure that builds up at the passenger compartment air inlet. The movement of the vehicle relative to the air it passes through will cause this pressure to increase as speed increases. This pressure increase tends to increase the air delivery through the climate control system when a voltage applied to the fan motor is held constant. On the other hand, vehicle testing has found that vehicle speed itself cannot be relied on to correctly maintain constant air delivery for various fan speeds. The original selected fan speed and the selected climate control unit temperature and air distribution (sometimes referred to as mode) doors present variables which must also be considered in the calculation to maintain constant air delivery.
None of the systems disclosed in the above-mentioned references address the above-referenced problem in a satisfactory manner.